Print this pageReactivation and Inversion Structures in Central Argentina
BOOTH, JACQUELINE L. M., and MIKE P. COWARD
Central Argentina shows a variety of basement-involved compressional
structures related to the Tertiary-aged Andean orogeny. The geometry and
kinematics of these faults and their related folds are quite distinct from the
more familiar style of thin-skinned fold-and-thrust belts. Two regions of the
country show particularly good examples - the Sierras Pampeanas terrane between
latitudes 27 degrees south and 33 degrees south, and the Neuquen Basin - 35 to
41 degrees south. The northwestern parts of the Neuquen Basin contain large
basement-cored anticlines, bound to their west by inverted normal faults, and on
the east by steeply dipping blind reverse faults, (50 to 60 degrees). This
second group of faults are unable to propagate through the syn-rift sequence and
displacement becomes transferred onto smaller backthrusts at the basement-cover
contact. Other basement-involved faults have produced large monoclines in the
basin-fill sequence. Where inversion can be recognized, back-rotation of the
Paleo-normal fault, footwall shortcutting, and expulsion of material out of the
half-graben can be identified.
The Sierras Panpeanas are a Precambrian-Palaeozoic terrane of basement blocks uplifted above the surrounding Neogene basins upon steep reverse faults which have reactivated the metamorphic fabric. Block rotations about vertical and horizontal axes have accompanied movement on the faults, which are of similar style to the Laramide uplifts of Wyoming.
Folding has preceded breakthrough of the thrusts, developing an anticline-syncline, the fault breaking through the common hinge.